Saxbyoceras kingpooli, Kröger, 2025

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 57-59

Saxbyoceras kingpooli gen. et sp. nov.

urn:lsid:zoobank.org:act:569E3891-BA40-49E8-A7BA-C29851D45C19

Fig. 23A–B

Diagnosis

Same as for genus, by monotypy.

Etymology

Refers to Kingpool, the tallest of the three figures in Eno Raud’s (1928–1996) children-book series “Naksitrallid”.

Type material

Holotype

ESTONIA • Vormsi Island , Saxby shore, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-25 .

Paratype

ESTONIA • 1 spec.; same data as for holotype; TUG 1745-245 .

Description

The holotype is a fragment of a slightly endogastrically curved conch consisting of a phragmocone and a mature body chamber. The external shell is partially preserved ( Fig. 23A ). The conch surface appears smooth but possesses faint narrowly spaced growth lines. In lateral view the body chamber is slightly curved with a straight margin on the prosiphuncular side and a convex margin on the antisphuncular side. It has a height of 78 mm at its base, and 89 mm at its aperture, and a maximum length of 48 mm. The peristome is too fragmentarily preserved to describe its complete outline but a shallow hyponomic sinus is visible on the prosiphuncular side. A faint ca 10 mm wide constriction occurs a few millimeters from the apertural conch margin.

The phragmocone expands from a height of 65 mm to 78 mm at a length of 41 mm (angle of expansion 18°). At a conch height of 65 mm, a conch width of ca 60 mm can be estimated (CHI = 1.1). The sutures are nearly straight transverse or with a shallow lateral lobe and are 10 mm apart where the conch height is 70 mm (RCL = 0.14). The septal foramen has a diameter of 12 mm and is located ca 17 mm from the concave conch margin where the conch height is ca 60 mm (RSH = 0.20, RSP = 0.35). The connecting ring is thick, the septal necks are short recumbent or achoanitic and no endosiphuncular deposits occur.

The second specimen is preserved only as two isolated phragmocone chambers with a conch height of 63–70 mm and a septal distance of 12 mm and 10 mm, respectively (RCL: 0.14–0.19). The sutures are directly transverse. The depth of the curvature of the septa is 14 mm where the conch height is 63 mm. The septal foramen is located in a distance of 20 mm from the conch margin with a diameter of 7 mm where the conch height is 63 mm (RSH = 0.11, RSP = 0.36). At a conch height of ca 60 mm, the siphuncular segments are expanded into the chambers with a rounded, convex shape in longitudinal section and with a maximum diameter of 11 mm where the chamber length is 8 mm (RSS = 1.38) and where the septal foramen is 3 mm. The segments have narrow circular adnate areas on the adoral and adapical surfaces of the septa (ca 2 mm wide). The connecting ring is thick, the septal necks are short recumbent or achoanitic and no endosiphuncular deposits occur.

Remarks

The specimens described above superficially, and with respect of the position and size of the septal foramen, are similar to specimens described by Eichwald (1860) under Orthoceras declive Eichwald, 1860 . However, because this species apparently combines type material of different taxa from the Middle Ordovician (collected in Tallinn) and from Katian strata (collected in Lyckholm) ( Eichwald 1860: 1206–1207) the species name cannot be used until the original material is revised.

Cyrtoceras substriatum Eichwald, 1860 , collected from Hohenholm (= Kõrgessaare; Hiiumaa) is probably related to S. kingpooli sp. nov., because of its similar conch shape and nearly central siphuncle (compare Teichert 1930: 271) but differs in having a transverse ornamentation.

Another species, which is possibly related to S. kingpooli sp. nov. is Faberoceras demshinense Balashov, 1975 from late Katian strata (Molodovskii horizon) of Podolia, Ukraine, which is a cyrtocone with a nearly central, widely expanded siphuncle. This species differs from S. kingpooli in having a more strongly curved conch and a transversely annulated ornamentation.

Family Diestoceratidae Foerste, 1926

Figures

Fig. 23. Saxbyoceras kingpooli gen. et sp. nov., holotype GIT 878-25 of the Vormsi Regional Stage, from Saxby shore, Vormsi Island, Estonia. A. Lateral view. B. Median section of the phragmocone with details of the siphuncle and connecting ring. Scale bars: A = 20 mm; B = 5 mm.